1. Field of the Invention
The invention relates to a hybrid motor vehicle and a method of controlling the hybrid motor vehicle. More particularly, the invention relates to a hybrid motor vehicle that includes: an internal combustion engine that outputs motive power; an engine-motoring electric motor that is able to motor the internal combustion engine; a vehicle traction electric motor that outputs motive power; and a secondary battery that supplies electric power to the engine-motoring electric motor and to the vehicle traction electric motor, and also relates to a method of controlling the hybrid motor vehicle.
2. Description of the Related Art
In relation to hybrid motor vehicles in which a rotary shaft of an electric motor is connected to an axle via the transmission, and an output shaft of an internal combustion engine is attached to the rotary shaft or the electric motor via a friction clutch, Japanese Patent Application Publication No. 11-205907 (JP-A-11-205907) describes a hybrid motor vehicle in which the friction clutch is gradually engaged to motor the engine, while the vehicle is powered by the electric motor, until the engine speed reaches about 200 rpm to 300 rpm before fuel injection and ignition are started to start the engine, and then the motive power from the engine is used for the traction of the hybrid motor vehicle. In the described hybrid motor vehicle, the shock caused when the engine is started is avoided by gradually increasing the rotational speed of the engine by gradually transmitting torque to the engine via the friction clutch.
In addition, Japanese Patent Application Publication No. 2008-190416 (JP-A-2008-190416) describes an internal combustion engine control apparatus for a hybrid motor vehicle, which has an electric motor that motors an internal combustion engine, that controls the electric motor turn the internal combustion engine in the reverse direction if the temperature of the internal combustion engine is below a threshold temperature when the internal combustion engine is to be started. According to the described control apparatus, it is possible to greatly reduce the electric power that the electric motor consumes in order to start the internal combustion engine, by turning the internal combustion engine in reverse, and injecting fuel into the atmosphere in a cylinder containing air, and igniting the injected fuel.
However, in the hybrid motor vehicle described in JP-A-11-205907, because the engine is motored at the time of being started, fuel may leak from fuel injection valves due to insufficient oil tightness, and may be directly discharged from the engine, so that undesirable emissions may increase. Likewise, in the hybrid vehicle described in (JP-A-2008-190416), if the temperature of the internal combustion engine exceeds the threshold temperature, the internal combustion engine is started by turning the engine in the normal rotational direction, so that fuel may leak from fuel injection valves due to insufficient oil tightness, and may be directly discharged from the engine.
In recent years, hybrid motor vehicles have been equipped with a secondary battery mounted in the vehicle that may be charged using an external electric power source when the vehicle is stopped. When, after the vehicle is started, the power needed for the traction of the vehicle is below an engine-starting power, which is set beforehand as a power that is used to start the internal combustion engine, the vehicle travels on the power from the vehicle traction motor without starting the internal combustion engine until the amount of electricity stored in the secondary battery has decreased to a prescribed level. When the power needed for the traction of the vehicle exceeds the engine-starting power while the vehicle is traveling on the power from the vehicle traction motor, the internal combustion engine is started and the power from the internal combustion engine is used for the traction of the vehicle. In this type of hybrid motor vehicle, because the internal combustion engine is required to output high power immediately after being started, the internal combustion engine is operated under high load and high rotational speed immediately after being started. However, in some cases, if the internal combustion engine is started for the first time after the system of the hybrid motor vehicle is started, the high-load and high-speed operation of the internal combustion engine may be performed the engine has been sufficiently lubricated by oil.